The  Tannic  Acid  of  Guar  ana. 
J  Am.  Jour.  Pharm. 
}       Aug.,  I877. 
excess  of  basic  acetate  of  lead  added,  which  threw  down  a  voluminous 
flesh-colored  precipitate.  This  was  thoroughly  washed  with  distilled 
water,  decomposed  by  sulphuretted  hydrogen  gas,  and  the  sulphide  of 
lead  removed  by  filtration.  The  filtrate,  after  being  heated  on  a  water 
bath  to  drive  off  the  excess  of  sulphuretted  hydrogen,  and  filtered, 
gave  a  clear  solution,  with  a  scarcely  perceptible  tinge  of  yellow. 
Evaporated  to  dryness,  this  solution  yielded  an  amorphous,  slightly 
yellow,  semi-transparent,  partially  scaly  mass,  which  had  the  peculiar 
taste  of  tannic  acid.  This  mass  dissolved  very  readily  in  alcohol,  and 
on  allowing  the  alcohol  to  evaporate  spontaneously,  it  was  still  found 
in  the  amorphous  condition.  That  it  is  not  incapable  of  crystallization, 
however,  was  proved  by  drying  a  small  quantity  of  the  aqueous  solution 
over  sulphuric  acid  under  a  bell-glass,  when  acicular  crystals,  radiating 
from  amorphous  centres,  were  formed. 
The  following  is  a  brief  description  of  the  behavior  of  this  acid  with 
different  reagents  : 
With  ferric  salts  it  gives  a  greenish  precipitate,  turning  to  brown  on 
standing  ;  with  ferrous  salts  no  precipitate  is  produced,  but  the  color  of 
the  liquid  is  changed  in  a  short  time  to  a  dark  green.  The  fixed  alkalies 
give  the  solution  a  dark,  reddish-brown  color  ;  with  ammonia  it  forms  a 
lighter  brown,  while  with  lime  water  it  gives  a  grayish-brown  precipitate. 
It  gives  a  green  precipitate  with  acetate  of  copper,  which  is  soluble  in 
an  excess  of  the  precipitant.  It  does  not  precipitate  the  neutral  sul- 
phate of  copper  solution,  but  reduces  the  alkaline  sulphate  slowly  in  the 
cold,  and  rapidly  when  heated  ;  it  also  reduces  nitrate  of  silver  by  the 
aid  of  heat,  and  decomposes  auric  chloride  in  the  cold.  It  gives  dull 
white  precipitates  with  barium  salts  (distinction  from  caffetannic  acid), 
and  a  white  precipitate  with  stannous  chloride.  It  resembles  caffetan- 
nic acid  in  not  precipitating  tartrate  of  antimony  and  potassa,  and  by 
readily  precipitating  both  cinchonia  and  quinia,  but  differs  from  it  in 
precipitating  gelatin  from  solution.  Its  reactions  with  the  alkaloids  and 
gelatin  serve  to  distinguish  it  from  catechuic  acid.  With  lead  acetate 
it  gives  a  dull  white  precipitate.  It  quickly  decolorizes  the  solution  of 
permanganate  of  potash,  and  gives  a  dark  red  color  with  molybdate  of 
ammonia,  which  is  discharged  by  oxalic  acid. 
It  produces  white  precipitates  with  morphia  and  strychnia,  and  with 
aconitina  and  veratria  with  hydrochloric  acid  ;  it  does  not  precipitate 
atropia,  either  in  neutral  solution  or  in  presence  of  an  acid.    It  gives 
